155016

We added up all the values from 7-15, then divided them by 3 because there are 3 values per line. This told us that each line should add up to 33, since we already had 2 values, 14 and 7, the other would have to be 12. Then, using the row with the 7 in it, the remaining numbers had to add up to 26, I picked 15 and 11, with 11 being in the middle. From this, we then used the 2 values from the diagonal with 12 and 11 in it and worked out that the other number must be 10 to make 33. After, we found that 9 was the answer that added to make 33 in the bottom row, 8 was the remaining number in the upper left corner, so n is 8.